Rain sensor, in particular for a motor vehicle

ABSTRACT

A rain sensor ( 10 ), in particular for a motor vehicle, is shown, having at least one transmitter ( 20 ) emitting radiation in the operating state, and at least one receiver ( 22 ) at least partially sensitive to the radiation from the transmitter ( 20 ), and a substantially flat light-conducting body ( 14 ) that is capable of being coupled nearly parallel to a surface of a wettable window pane ( 12 ) of the motor vehicle, and comprising structures ( 18   a,    18   b ) for directing and catching the radiation from the transmitter ( 20 ), whereby the structures ( 18   a ) for directing the radiation are different from the structures ( 18   b ) for catching the radiation, and they have radiation-concentrating properties.

BACKGROUND OF THE INVENTION

[0001] The invention concerns a rain sensor according to the generalclass of the independent claim. Numerous rain sensors have already beenmade known, for example in DE 198 15 748 A1, that measure the wetting ofthe windshield of a motor vehicle with the aid of a transmitter and areceiver via the principle of total reflection. Said rain sensorscomprise a light-conducting body that is designed substantially flat inshape and is arranged on the interior of the motor vehicle nearlyparallel to the surface of the windshield.

ADVANTAGES OF THE INVENTION

[0002] The rain sensor according to the invention having the features ofthe main claim has the advantage that the respective focussing needs canbe taken into account by means of various structures for directing andcatching radiation, by way of which the sensitivity of the rain sensoris improved.

[0003] Advantageous further developments and improvements of thefeatures indicated in the main claim result from the measures listed inthe dependent claims.

[0004] It is particularly advantageous when the structures for directingthe radiation toward the window pane are spherical in character, and thestructures for catching the radiation are non-spherical in character. Inthis fashion, a maximum amount of light is directed toward thewindshield and, simultaneously, only the radiation relevant to themeasurement of precipitation is reflected by the windshield. Thisincreases the size of the the measuring regions on the windshield,therefore increasing the signal-to-noise margin of the rain sensorsignal.

[0005] If the structures for directing the radiation are formed asspherical segments, they are very easy to produce as sphericalstructures, in particular when the light3 conducting body is aninjection-molded part.

[0006] It is furthermore advantageous when the structures for catchingthe radiation comprise cylindrical segments, the cover surface of whichis formed as a non-spherical lens. The cylindrical segments bring abouta shield-like effect, so that only the desired radiation can passthrough the light-conducting body to the receiver. The non-sphericallenses make it possible to move the receivers closer to thelight-conducting body than would be possible with spherical lenses.

[0007] It is particularly advantageous when the concentrated beams meetoutside of the geometrical center line of the cylindrical segment. Dueto this squinting lens, the optical components such as transmitter andreceiver can be moved even closer to the light-conducting body, whichfurther reduces the proportions of stray illumination.

[0008] If the surface of the light-conducting body capable of beingcoupled to the window pane comprises a slight convex arch, air bubblesthat can form in the coupling region when the light-conducting body iscoupled to the window pane are advantageously prevented. Additionally,tension is produced over the entire light-conducting body duringinstallation, with the effect that changes in shape due to temperatureor ageing, for example, can be offset.

[0009] If multiple structures for directing and catching radiation areprovided in each case that are arranged in pairs in each case, aplurality of measuring paths can be arranged on the narrowest space, andthe dimensions of the rain sensor can be limited to a minimum. This isparticularly advantageous because the rain sensor can be arranged on thewindshield in such a fashion that it does not obstruct the driver'svision.

[0010] It is particularly advantageous when four structures each areprovided for directing and catching radiation that are arranged in sucha fashion that the measuring paths form a parallelogram when projectedonto the window pane. By means of such an arrangement, four measuringpaths can be realized using two transmitters and two receivers, wherebysufficient space is available in the center of the parallelogram forarranging a further sensor or a heating device, for example.Additionally, due to the fact that each transmitter transmits inmultiple measuring paths and each receiver receives from multipledirections, costly optical semiconductor components can be spared.

[0011] If the surface of the light-conducting body capable of beingcoupled to the window pane is at least partially provided with onecomponent of a multiple-component adhesive, the light-conducting bodycan be installed quickly and securely to the window pane.

SUMMARY OF THE DRAWINGS

[0012] An exemplary embodiment of the invention is presented in thedrawing and described in greater detail in the subsequent description.

[0013]FIG. 1 shows a sectional drawing of a rain sensor according to theinvention, and

[0014]FIG. 2 shows a perspective view of a light-conducting body of arain sensor according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A sectional drawing of a rain sensor 10, according to theinvention, on a window pane 12 is shown in FIG. 1. The rain sensor 10comprises a light-conducting body 14 that forms a cover of the rainsensor 10. With this light-conducting body 14, the rain sensor 10 isadhered to the window pane 12 via a coupling medium 16. A non-adhesivecoupling medium can also be used, of course, if the fastening isperformed via a separate fastening device, for example.

[0016] The light-conducting body 14 comprises structures 18 a, 18 b thatdirect the light from the transmitter 20 via the coupling medium 16toward the window pane 12 and catch the light totally-reflected by thewindow pane 12 via the coupling medium 16 once again and direct it tothe receiver 22. Transmitter 20 and receiver 22 are arranged on a commonboard 24 formed as a printed-circuit board. This board 24 is arranged inthe rain sensor 10 inside a housing 25 nearly parallel to the windowpane 12, in such a manner, in fact, that the transmitter 20 and thereceiver 22 are mounted nearly over the structures 18 a, 18 b. For thispurpose, the light-conducting body can also comprise not shown domesthat can grip in corresponding bores in the board 24 and in this fashionmake it easier to mount the transmitter and receiver on the structures18 a, 18 b. The receiver 22 and/or transmitter 20 are mounted in such afashion, of course, that the sensitive regions of the receiver 22 and/orthe transmitter 20 are arranged in such a manner as to obtain maximumsensitivity in the focussing region of the radiation-concentratingstructures 18 a, 18 b.

[0017] The radiation from the transmitter 20 is directed toward thewindow pane 12 at an angle of approximately 45°, reflected at leastpartially on the wettable surface of the window pane 12 depending on theamount of wetting and reflected by the window pane 12 at an angle ofapproximately 45°, and sent to the receiver 22.

[0018] The housing 25 can also comprise lobes 26 on its outside thatserve to put a second housing over the entire rain sensor 10, inparticular when special requirements are placed on the housing. Thisalso applies, of course, independently of the special design of thelight-conducting body 14.

[0019]FIG. 2 shows a perspective view of a light-conducting body 14 indetail. Said light-conducting body is substantially rectangular in shapeand provided with a circumferential groove 28. Further fasteningelements 30 are also arranged in the region of this groove 28 thatfasten the light-conducting body to the housing. The light-conductingbody comprises the domes 32 for mounting the board 24 shown in FIG. 1,which said domes rise out of the light-conducting body 14 cylindricallyperpendicular to the window pane 12. The structures 18 a, 18 b arearranged in pairs in each case nearly in the center of the rectangle ofthe light-conducting body 14. The structures 18 a serve to direct theradiation from the transmitter 20, and the structures 18 b serve tocatch the radiation totally-reflected by the window pane and focus it onthe receiver 22.

[0020] The structures 18 a, which serve to direct the radiation, areformed as spherical segments that lie directly on the flat base surface34 of the light-conducting body 14. Since the transmitters 20 arearranged over the structures 18 a, distant beams are also stillrefracted in the direction of the window pane 12, which increases thetotal amount of radiation directed toward the window pane in relation tothe lens structure according to the related art.

[0021] The structures 18 b, which serve to catch and focus the radiationon the receiver 22, substantially comprise a cylindrical segment 36, onthe cover surface of which a non-spherical lens 38 is integrally molded.Since the totally-reflected radiation—which reflects the measuringsignal—is to be focussed on the receiver 22 with the greatest possibleaccuracy, these non-spherical structures 18 b are particularlywell-suited for catching radiation. The non-spherical lens is therebyshaped and arranged in such a fashion that its focussing region exactlyfills the sensitive surface of the receiver 22.

[0022] By arranging the structures 18 a and 18 b in pairs, fourmeasuring paths are produced with the aid of two transmitters 20—each ofwhich is arranged nearly over one structure pair 18 a—and tworeceivers—each of which is arranged nearly over one structure pair 18 b,which said measuring paths form a parallelogram when projected onto thewindow pane 12. In this fashion, additional installation space isavailable in the center of the parallelogram in which a further sensor,e.g., a luminosity sensor or a temperature sensor, can be arranged. Thearrangement of a heating element for heating the sensor device or thewindow pane 12 in the measuring region is also feasible. If an opticalsensor is arranged in this central region, said optical sensor can beoptically separated from the measuring paths, e.g., by means of ridgesraised in the manner of a wall, in order to prevent any disturbances ofthe precipitation measurements by irradiation of daylight. This isindependent of the special design of the structures 18 a and 18 b,however. It is also possible, of course, to form the structures 18 a, 18b not in the fashion of a lens, as shown in the Figures, but in thefashion of a mirror. A mixed design is also feasible, in which oneportion of the structures 18 a are formed in the fashion of a lens fordirecting radiation, and a further portion is formed in the fashion of amirror. The same applies as well for the structures 18 b for catchingradiation, of course.

What is claimed is:
 1. A rain sensor (10), in particular for a motorvehicle, having at least one transmitter (20) emitting radiation in theoperating state, and at least one receiver (22) at least partiallysensitive to the radiation from the transmitter (20), and asubstantially flat light-conducting body (14) that is capable of beingcoupled nearly parallel to a surface of a wettable window pane (12) ofthe motor vehicle, and comprising structures (18 a, 18 b) for directingand catching the radiation from the transmitter (20), wherein thestructures (18 a) for directing the radiation are different from thestructures (18 b) for catching the radiation, and they compriseradiation-concentrating properties.
 2. The rain sensor (10) according toclaim 1, wherein the structures (18 a) used to direct the radiation arespherical in character, and the structures (18 b) used to catch theradiation are of non-spherical character.
 3. The rain sensor (10)according to claim 1 or 2, wherein the structures (18 a) for directingthe radiation are formed as a spherical segment.
 4. The rain sensor (10)according to one of the preceding claims, wherein the structures (18 b)for catching the radiation have a cylindrical segment, and the coversurface is formed as non-spherical lens.
 5. The rain sensor (10)according to one of the preceding claims, wherein the structures (18 b)for catching the radiation comprise a cylindrical segment, in particulara slanting cylinder segment, through which a geometrical center line iscapable of being construed, in particular parallel to the cover surfaceof the cylindrical segment, and the regions in which the caughtradiation is concentrated lie outside of the [geometrical center line].6. The rain sensor (10) according to one of the preceding claims,wherein the surface of the light-conducting body capable of beingcoupled to the window pane (12) has a convex arch.
 7. The rain sensor(10) according to one of the preceding claims, wherein a plurality ofstructures (18 a, 18 b) for directing and catching radiation areprovided that are arranged in pairs in each case.
 8. The rain sensor(10) according to one of the preceding claims, wherein four structures(18 a, 18 b) each are provided for directing and catching radiation,which said structures are arranged in such a fashion that the beam pathsdetermined by the arrangement of the structures (18 a, 18 b) form aparallelogram when projected onto the window pane (12).
 9. The rainsensor (10) according to one of the preceding claims, wherein thesurface of the light-conducting body (14) capable of being coupled tothe window pane (12) is at least partially provided with one componentof a multiple-component adhesive.
 10. The rain sensor (10) according toone of the preceding claims, wherein a plurality of structures (18 a, 18b) is associated with one transmitter (20) in each case and/or onereceiver (22) in each case.